CMC Cheat Sheet 2026

The 30 highest-yield CMC facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. Under NFPA 306, which person is qualified to issue a marine chemist certificate? → A National Fire Protection Association (NFPA) licensed marine chemist
2. After gas freeing, a Marine Chemist tests a tank and finds oxygen at 20.9%, LEL at 0%, and no toxic gases detected. The certificate issued should be: → Safe for workers — Hot Work and Cold Work
3. Which of the following is considered 'hot work' under NFPA 306 and requires Marine Chemist certification? → Electric arc welding on a bulkhead adjacent to a cargo tank
4. What is the ACGIH TLV-TWA for benzene? → 1 ppm
5. According to NFPA 306, which of the following locations requires a Marine Chemist's certificate before commencing hot work? → On a pipeline connected to a fuel tank that has been emptied and cleaned.
6. Under OSHA 29 CFR 1910.146, which condition by itself classifies a space as a 'permit-required confined space'? → The space has an internal atmosphere that could contain a serious safety or health hazard
7. When sampling a large cargo hold for atmospheric hazards, the marine chemist should prioritize testing at which locations? → Multiple levels including low, mid, and high points plus remote corners
8. A gas detector is bump-tested before use. What does a bump test verify? → That the instrument alarms respond to a known gas concentration
9. What is the minimum oxygen concentration by volume required in a cargo tank atmosphere before personnel may enter for cleaning or inspection? → 19.5% by volume
10. According to NFPA 306, what minimum oxygen concentration is required for a space to be certified 'Safe for Workers' without respiratory protection? → 19.5% by volume
11. Which UN hazard class covers corrosive substances such as sulfuric acid when transported aboard a vessel? → Class 8 — Corrosive Substances
12. When testing a deep or stratified atmosphere within a permit-required confined space, what is the OSHA-recommended practice for positioning the sampling probe? → Test at approximately 4-foot intervals in the direction of travel and to each side.
13. Inerting a cargo tank to prevent flammable atmosphere buildup is achieved when the oxygen content is reduced to below: → 8%
14. A Marine Chemist inspecting a ballast tank adjacent to a cargo hold that last carried gasoline should perform the FIRST atmospheric test for: → Flammable vapors using a calibrated combustible gas indicator
15. A Marine Chemist inspecting a tank that previously carried crude oil finds an LEL reading of 8%. Which certificate designation is correct under NFPA 306? → 'Not Safe for Hot Work — Safe for Men'
16. When obtaining a representative bulk liquid sample from a marine cargo tank containing a homogeneous liquid, the preferred sampling point is: → Mid-depth of the liquid column to capture the most representative stratum
17. Slag from overhead welding falls into an open void space during authorized hot work. What is the IMMEDIATE required response? → Stop hot work and inspect the void space for fire or smoldering material
18. The NIOSH IDLH value for carbon monoxide (CO) is: → 1200 ppm
19. In the CMC continuing education requirement, which activity typically qualifies for professional development hours? → Attending MCA-approved technical seminars or completing relevant coursework
20. A cargo tank last carried crude oil is being prepared for hot work. Under NFPA 306, what type of cleaning process is necessary to achieve a gas-free condition? → Tank washing followed by thorough ventilation to reduce vapors below LEL limits
21. Under 33 CFR Part 155, vessel owners must maintain an Oil Spill Response Plan (OSRP) that is reviewed and resubmitted to the USCG every: → 5 years
22. Under EPA regulations (40 CFR Part 112), facilities handling oil above threshold quantities must prepare a: → Spill Prevention Control and Countermeasure (SPCC) Plan
23. What role does the SOLAS Convention play in maritime safety? → SOLAS sets regulations for life-saving equipment and safety measures on ships.
24. When a hazardous material spill occurs in a vessel's bilge, the FIRST action under MARPOL Annex I is to: → Transfer the mixture to a slop tank and prevent overboard discharge
25. A Marine Chemist is called to re-certify a tank after hot work was suspended for lunch. What is required before re-issuing the certificate? → A full atmospheric re-test of the work space and all adjacent spaces
26. A Marine Chemist is sampling ballast water for oxygen content. Which instrument provides a real-time continuous measurement rather than a grab sample reading? → Electrochemical oxygen analyzer with in-line probe
27. Which gas detection instrument is most appropriate for measuring hydrogen sulfide (H₂S) at sub-ppm concentrations in a confined marine space? → Electrochemical sensor calibrated for H₂S
28. Which document must a Certified Marine Chemist issue before hot work is permitted in or near a confined space on a vessel? → Certificate of Fitness
29. The Threshold Limit Value–Ceiling (TLV-C) for a substance differs from TLV-TWA in that it: → Must never be exceeded even instantaneously
30. What is 'clingage' in the context of cargo tank cleaning operations? → Cargo residue that adheres to tank surfaces and cannot be removed by pumping alone